Serum 25(OH)D and sun exposure assessmentīlood sample was drawn by a trained phlebotomist by venipuncture after 10–12 h overnight fast. If the selected individual could not be contacted in three visits, that person was excluded from the study. Following this, the required number of samples was drawn from the sampling frame from each village using the simple random sampling method.

Women aged 60 years and above were selected from villages, and the number of participants from each village was calculated by population proportionate to size method. In the first stage, 30 villages were selected randomly from 80 total villages of Amdanga block. Finally, 236 participants could be covered. Additional 10% was added to compensate the dropout and finally, it was calculated to be 239. Since multistage random sampling was adopted, it was multiplied by 1.5 (design effect), which came out to be 217.5. The calculated sample size came out to be 145.

The sample size was calculated by taking the previous prevalence of Vitamin D deficiency as 91.2% and using formula n = (Z (1-∞/2))²pq/L² where L is allowable error, which was taken as 5% of p, and Z (1-∞/2) is the standard normal deviate at 95% confidence limit, which was 1.96. Sample size calculation and sampling technique With this background, the present study was conducted to find out the association between the period of sun exposure and Vitamin D status among the rural elderly women of West Bengal. Vitamin D deficiency has been found to be prevalent among Indian elderly women. High prevalence of Vitamin D deficiency was observed in India across different age groups and both sexes. Thus, reduced renal production of 1,25-dihydroxyvitamin D as well as decreased intake of fortified foods also pose great difficulties in Vitamin D formation in body. Moreover, reduced mobility or institutionalization causing reduced sun exposure. It has been observed that 70 years old had about 25% of the 7-dehydrocholesterol in comparison to a young adult and thus had 75% reduced capacity to make Vitamin D3 in the skin. Aging has significant association with decreased concentrations of 7-dehydrocholesterol, the precursor of Vitamin D3 in the skin.

Maximum Vitamin D production reached after 10–15 min of sun exposure, especially during summer, while one erythema dose is achieved which is equivalent to intake of over 500 µg of Vitamin D3. The principal source of Vitamin D among the human population is exposure of the skin to ultraviolet B (UVB) radiation (290–315 nm).

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